Fuel pumps for use in conduction with gas turbine engines

ABSTRACT

A fuel pump in which there is provided a centrifugal impeller operative at high speed and a reciprocating piston pump operative at low speeds. The pump becomes inoperative when a speed is reached such that the spring loading of the pistons is overcome by the pressure generated by the centrifugal impeller. The outlets of the two pumps are connected together via non-return valves.

United States Patent 1 [1 1 Lewis I [11'] 3,811,797 [4'51 May21, 1974 [5 FUEL'PUMPS FOR USE IN 'CONDUCTION WITH GAS TURBINE ENGINES [75] Inventor: Geoffrey Arthur Lewis, Solihull,

England [73] Assignee: Joseph Lucas (Industries) Limited,

Birmingham, England Filed: July 31, 1972 Appl. No.: 276,440

References Cited UNlTED STATE-S PATENTS 2,612,844 10 1952 Grise....'........ ..417/20 lnt.-Cl. F04b 23/08 2,292,896 8/1942 Morgan 417/202 2,666,393 l/l954 Troeger et al. 1. 417/202 2,982,215 5/1961 Baker 9 H503 FOREIGN PATENTS OR APPLICATIONS 1,004,080 9/1965 Great Britain 417/214 Primary Examiner-William L. Freeh Assistant Examiner-Gregory Paul LaPointe Attorney, Agent, or Firm-Holman & Stern [5 7 ABSTRACT A fuel pump in whichlthere is provided a centrifugal impeller operative at high speed and a reciprocating piston pump operative at low speeds. The pump becomes inoperative when a. speed is reached such that the spring loading of the pistons is overcome by the pressure generated by" the centrifugal impeller. The outlets of the two pumps are connected together via non-return valvesf I: 3 Claims, 2 Drawing Figures g to 14 29 l6 32 I3 2 9 up a 42s I5 22 ,:l "'H FUEL PUMPS FOR USE IN CONDUCTION WITH GAS TURBINE ENGINES BACKGROUND OF THE INVENTION SUMMARY or Tl-IEINVENTION A fuel pump in accordance with the invention comprises a housing having an inlet and a chamber into which the inlet opens, a rotor in said housing, said rotor including a centrifugal impeller in the chamber in the housing, a first outlet communicating with said chamber, a first non-return valve controlling said first outlet, a plurality of pistons slidable in bores in the housing opening at one end into the chamber, cam means on said impeller engageable with said pistons for reciprocating said pistons in said bores as the rotor is rotated, resilient means urging said pistons in a direction towards the chamber, a second outlet in the housing, passage means in the housing and rotor connecting said bores to said. inlet and to the second outlet, and a second non-return valve controlling-said second outlet, said first and second outlets being interconnected.

' An exampleof the invention is illustrated diagrammatically in the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinalsection through the pump,

chamber has a wall 13 opposite the inlet 12 and a plurality of bores 14- parallel to and equally spaced from the axis of the chamber 12 are formed inthis wall so as to open into the chamber. An axial bore l'extends' through thehousing and a series of cross bores 16 connect this axial bore with the respective bores 14.

Mounted in suitable bearings (not shown) in the housing is a rotor'l7. This rotor comprises a shaft portion 18 extending through the bore 15 and a centrifugal impeller 19 on one end of the shaft portion 18 and dis posed within the chamber 12. The centrifugal impeller 19 includes a disc portion 20, and a plurality of vanes 21 on one side of the disc portion 20. The vanes 21 extend radially inwards to a radius greater than that of the inlet 11. The shaft portion 18 is formed with a pair of recesses 22, 23 at an axial position corresponding to the position of the cross bores 16 in the housing. Each recess 22, 23 extends circumferentially around the 'thereon with its axis inclined to the axis of the rotor.

This annulus 28 forms cam means co-acting with pistons 29 slidable in the bores 14, with each piston being spring loaded as at 29a towards the annulus 28. The

' plane of the inclined annulus 28 is arranged so that each piston 29 is displaced thereby further into the associated bore 14 when the associated cross bore 16 is between one pair of adjacent ends of the recesses 22, 23.

A main outlet 30 of the pump communicates with the periphery of the chamber 12 and is controlled by a first non-return ,valve 31. A second outlet 32 of the pump is connected to the groove 27 and is controlled by a second non-return valve 33. The two outlets are connected together.

In use, the pump may be connected directly to a shaft of a gas turbine engine without any reduction gearing. The centrifugal impeller 19 is designed to give sufficient pressure at the maximumspeed of the engine to satisfy the demands of the fuel system. It will be appreciated, however, that since the delivery pressure of centrifugal pump varies with the square of the speed, the

' centrifugal impeller may not be capable of supplying sufficient pressure at low speed. In addition, centrifugal pumps are not self-priming.

The inclusion of the reciprocating piston pump arrangement improves the low speed characteristics of the pump and also renders the pump capable of priming itself. At low speeds the pistons 29 are reciprocated by the action of the inclined annulus 28 and fuel is pumped thereby from the inlet 11 to the outlet 32. The pressure at the periphery of the chamber 12 is lower than that in the groove 27 so that the non-return valve 33 opens but the valve 31 closes. As the speed increases, the pressure at the periphery of thechamber increases and when this exceeds the pressure in the groove 27 sufiiciently to overcome the spring-loading of the pistons 29, the latter are urged by the pressure out of engagement with the annulus 28. Thus at highspeed, loads on the pump caused by the pumping action of the pistons 29 are avoided.

I claim:

ll. A fuel pump comprising a housing having an inlet and a pumping chamber into which the inlet opens, a rotor in said housing, said rotor including a centrifugal impeller in the pumping chamber in the housing, a first outlet communicating with said chamber, a first nonretum valve controlling said first outlet, a plurality of pistons slidable in bores in the housing opening at one end into the chamber, cam means on said impeller engageable with said pistons for reciprocating said pistons in said bores as the rotor is rotated,'resilient means urging said pistons in a direction towards the chamber, a second outlet in the housing, passage means in the housing'and rotor connecting said bores to said inlet and to the second outlet, and a second non-return valve controlling said second outlet,'said first and second outlets being interconnected, the arrangement being such that at low speeds, the pistons are reciprocated by the cam means and fuel is pumped from the inlet to the second outlet as the pressure at the periphery of the pumpingchamber is lower than the passage means in the housing so that the second non-return valve opens and the first non-return valve closes, and as speed in-- creases, the pressure at the periphery of the pumping chamber increases and when the same exceeds the pressure in the passage means in the housing sufficiently to overcome the action of the resilient means, the pistons are urged by the pressure out of engagement with the cam means thereby avoiding loads on the pump caused by the pumping action of the pistons.

2. The fuel pump as claimed in claim 1 in which said bores extend in a direction parallel to the axis of the rotor, which includes a shaft portion extending along an axial bore in the housing, said bores being connected to said axial bore by cross bores in the housing and said shaft portion having recesses therein whereby said cross-bores are successively connected to the inlet and said second outlet as the rotor is rotated.

3. A fuel pump for use with gas turbine engines comprising a housing having an inlet and a pumping chamber into which the outlet opens, a rotor in the housing, the rotor having a shaft portion extending along an axial bore in the housing, a centrifugal impeller carried by the shaft portion and being located in the pumping chamber, a plurality of pistons slidable in bores in the housing, said bores extending in a direction parallel to the axis of the shaft portion of the rotor and opening at one end into the pumping-chamber, cam means on the impeller engageable with said pistons for reciprocating said pistons in said bores as the rotor is rotated, resilient means urging said pistons in a direction towards the pumping chamber, a first outlet in the housing communicating with the periphery of the pumping chamber, a first non-return valve controlling the first outlet, a second outlet in the housing,.a second non-return valve controlling said second outlet, means connecting said first and second outlets, the bores for the pistons communicating with cross bores in the housing, said shaft portion having a pair of recesses at an axial position corresponding to the position of the cross bores, each recess extending circumferentially around the shaft portion through an angle somewhat less than axial passage means inthe shaft portion connecting one of the recesses to the inlet, said shaft portion having an axial groove, said housing having a groove connected to the second outlet and to said axial groove in the shaft portion, and means connecting the axial groove in the shaft portion to the other recess. the arrangement being such that at low speeds, the pistons are reciprocated by the action of the cam means on the impeller and fuel is pumped from the inlet to the second outlet as the pressure at the periphery of the pump-' ing chamber is lower than that in the groove in the housing so that the second non-return valve opens and the first non-return valve closes, and as speed increases, the pressure at the periphery of the pumping chamber increases and when the same exceeds the pressure in the groove in the housing sufficiently to overcome the action of the resilient means, the pistons are urged by the pressure out of engagement with the cam means thereby avoiding loads on the pump caused by the pumping action of the pistons. 

1. A fuel pump comprising a housing having an inlet and a pumping chamber into which the inlet opens, a rotor in said housing, said rotor including a centrifugal impeller in the pumping chamber in the housing, a first outlet communicating with said chamber, a first non-return valve controlling said first outlet, a plurality of pistons slidable in bores in the housing opening at one end into the chamber, cam means on said impeller engageable with said pistons for reciprocating said pistons in said bores as the rotor is rotated, resilient means urging said pistons in a direction towards the chamber, a second outlet in the housing, passage means in the housing and rotor connecting said bores to said inlet and to the second outlet, and a second non-return valve controlling said second outlet, said first and second outlets being interconnected, the arrangement being such that at low speeds, the pistons are reciprocated by the cam means and fuel is pumped from the inlet to the second outlet as the pressure at the periphery of the pumping chamber is lower than the passage means in the housing so that the second non-return valve opens and the first non-return valve closes, and as speed increases, the pressure at the periphery of the pumping chamber increases and when the same exceeds the pressure in the passage means in the housing sufficiently to overcome the action of the resilient means, the pistons are urged by the pressure out of engagement with the cam means thereby avoiding loads on the pump caused by the pumping action of the pistons.
 2. The fuel pump as claimed in claim 1 in which said bores extend in a direction parallel to the axis of the rotor, which includes a shaft portion extending along an axial bore in the housing, said bores being connected to said axial bore by cross bores in the housing and said shaft portion having recesses therein whereby said cross-bores are successively connected to the inlet and said second outlet as the rotor is rotated.
 3. A fuel pump for use with gas turbine engines comprising a housing having an inlet and a pumping chamber into which the outlet opens, a rotor in the housing, the rotor having a shaft portion extending along an axial bore in the housing, a centrifugal impeller carried by the shaft portion and being located in the pumping chamber, a plurality of pistons slidable in bores in the housing, said bores extending in a direction parallel to the axis of the shaft portion of the rotor and opening at one end into the pumping chamber, cam means on the impeller engageable with said pistons for reciprocating said pistons in said bores as the rotor is rotated, resilient means urging said pistons in a direction towards the pumping chamber, a first outlet in the housing communicating with the periphery of the pumping chamber, a first non-return valve controlling the first outlet, a second outlet in the housing, a second non-return valve controlling said second outlet, means connecting said first and second outlets, the bores for the pistons communicating with cross bores in the housing, said shaft portion having a pair of recesses at an axial position corresponding to the position of the cross bores, each recess extending circumferentially around the shaft portion through an angle somewhat less than 180*, axial passage means in the shaft portion connecting one of the recesses to the inlet, said shaft portion having an axial groove, said housing having a groove connected to the second outlet and to said axial groove in the shaft portion, and means connecting the axial groove in the shaft portion to the other recess, the arrangement being such that at low speeds, the pistons are reciprocated by the action of the cam means on the impeller and fuel is pumped from the inlet to the second outlet as the pressure at the periphery of the pumping chamber is lower than that in the groove in the housing so that the second non-return valve opens and the first non-return valve closes, and as speed increases, the pressure at the periphery of the pumping chamber increases and when the same exceeds the pressure in the groove in the housing sufficiently to overcome the action of the resilient means, the pistons are urged by the pressure out of engagement with the cam means thereby avoiding loads on the pump caused by the pumping action of the pistons. 